1. Technical Field
The present invention is directed toward isolators, and more particularly toward a ventilation system for isolators which control the environment of animals for experimental purposes.
2. Background Art
As medical science has progressed, the production of laboratory animals in germ-free (axenic) status has become desirable in order to obtain more statistically significant laboratory experiments. The maintenance of animals in long-term studies requires a consistent uniform environment. Also, it has become important to protect workers caring for the laboratory animals from the environment in which the laboratory animals are subjected, not only for safety reasons (for example, to protect workers from asbestos fibers, aerosols, or other toxic substances which may be either inhaled or absorbed by skin contact) but also in order to obtain valid interpretable test results with the animals.
A number of different types of isolators have been developed which encapsulate a cage or system of cages to separate the environment of the animals from that of the workers.
One isolator type includes a clear plastic enclosure which encapsulates a metal framework supporting a number of cages. Typically, these isolators are ventilated by introducing suitably filtered air through one or two ports and outletting the air through an exhaust port located elsewhere in the enclosure. However, even with such ventilation systems, there can be stagnant areas in the isolator, so that cages in those areas will not be properly ventilated. Proper ventilation is important not only to provide proper air to the animals but also to prevent the cages from becoming messy (for example, the animal urine will not suitably dry out without adequate ventilation). While the aesthetics of having a few "messy" cages may be of minimal importance, such different conditions in different cages within the same isolator could undesirably effect test results by making one of the most crucial presumptions of most such tests (i.e., that all of the animals were maintained in an identical environment) false.
Individual isolator cages equipped with a filter mechanism on the top of the cage controlling the quality of air to that respective cage have also been used. The filters used with these cages can, however, undesirably restrict the ventilation to each cage since the air is allowed to pass through the filter, but is not forced through. Further, such cages can be relatively expensive due to the requirement the each cage have its own filter structure. Still further, undesirably different environments can exist in different cages if each filter on each cage does not operate identically (an unlikely occurrence due to the changing air permeability of the filter media over time in each filter). As noted above, such different environments can negatively effect, or even invalidate, test results.
Yet another structure has been used includes individually isolated cages which are connected to a manifold providing a common air source for forced ventilation. While this structure can increase the flow and ventilation within the cage over that occurring in the individually filtered cages described above, it can produce an unhealthy draft in each cage. Further, this structure requires connectors for sealing each cage to the air source (which connectors must be constructed of a durable material which will not be damaged if chewed on by the animals), and therefore can be very expensive, particularly where large numbers of cages are needed. Still further, exacting handling of each cage is required in order to ensure that the connection of the cage to the air source is properly sealed each time a cage is added to the air source manifold. Failure to properly handle such cages can result in different environments in different cages and thereby negatively effect test results as discussed above.
The present invention is directed toward overcoming one or more of the problems discussed above.